Basic Block Size

Choosing the XDR block size requires a tradeoff. Choosing a small size
such as 2 makes the encoded data small, but causes alignment problems for
machines that are not aligned on these boundaries. A large size such as 8
means the data is aligned on virtually every machine, but causes the encoded
data to grow too large. Four was chosen as a compromise. Four is big enough
to support most architectures efficiently.

This basic block size of 4 does not mean that the computers cannot utilize
standard XDR, just that they do so at a greater overhead
per data item than 4-byte (32-bit) architectures. Four is also small enough
to keep the encoded data restricted to a reasonable size.

The same data should encode into an equivalent result on all machines
so that encoded data can be compared or checksummed. So, variable-length data
must be padded with trailing zeros.